Anyone calibrate their monitoring gain?
Jun 10, 2007 at 4:43 PM Thread Starter Post #1 of 4

ofajen

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I didn't see a thread on this, so here goes...

The broad questions are:

1) do you try to consistently set HP monitoring levels?

2) do you try to qualitatively or quantitatively adjust for the "loudness" (degree of compression) of the program material? and finally

3) do you set your monitoring level according to a reference level?

I'm just curious if any folks here use calibrated monitoring gain in their HP listening, where gain is referenced to an SPL standard and gain is adjusted based upon the loudness (degree of compression) of the program material.

The practice I use with my studio monitors comes mainly from the excellent work of mastering engineer Bob Katz. I haven't yet adopted fully equivalent practices with HP but will be able to after I buy a HP amp.

The precise control of monitoring gain is most critical for mastering, where the overall loudness of a mix is adjusted, but I find it very useful in both tracking and mixing in order to get a proper sense of dynamics and loudness from the beginning rather than trying to fix things after the fact. It's also pretty handy when just listening in order to keep listening levels from getting out of hand.

I use it as a consistent practice with my studio monitors, but haven't been as quantitative with HPs, I've just tried to use about the same gain setting most of the time, while turning down "a bit" for really loud material.

As you probably know, perceived loudness is genereally proportional to RMS or averaged signal power and has little to do with instantaneous peaks. Katz' system, known as the K System is incorporated as a digital metering standard by a number of the better digital meter and digital meter plug-in makers. K-20, meaning that 0dBFS is 20 dB above the reference level is used for uncompressed material (audiophile, classical, etc. and some mixes of material that will be further compressed during mastering).

I tend to mix using the K-20 system and leave the decisions about compression for the final, mastering stage. K-14 is intended for most somewhat-compressed program material and has 14 dB from reference level to 0 dBFS. K-12 is intended for heavily compressed broadcast programming.

Using the K-System and calibrated monitoring gain allows you to maintain consistent monitoring levels. I use this system with my main studio monitors. I use a custom made stepped attenuator with 20 steps of 1 dB each. I calibrate the 0 dB (no attenuation) setting to produce 83 dB SPL at the listening position with one speaker or 86 dB with both speakers driven when I play a calibrated -20 dBFS noise file. This is known as the RP-200 standard and is widely used in the sound for film world and audio mastering in order to get sound levels that are consistent and "right".

Generally, you listen to K-20 (quiet, uncompressed, dynamic) material with the gain up around 0 dB, while typical, compressed material would have a gain setting of about -6 dB down to hopefully no lower than -9 dB, because lower settings imply such over use of compression that the end result is likely to be seriously degraded audio.

I'm planning to use that same attenuator to calibrate monitor gain on HPs, too, which will require a headphone amp and a switch to route the attenuated signal to mains amp or HP amp (or perhaps merely a multed attenuator output to both amps if that can work). I have to buy a separate headphone amp because even if I use the same stepped attenuator that I use in front of the monitor amp, it will have to be in front of the headphone amp, not after it, since the impedance of the headphones varies with frequency and the stepped pot won't really work properly there.

The other needed step is to actually calibrate the HP levels to the same SPL reference level. I've tried an SPL meter inside the headphones to do the same sort of calibration, but I think I get more accurate results by simply using the sensitivity rating of the headphones to determine the appropriate output voltage level to produce the right signal level. Example: HD580 sensitivity is 1 mW produces 97 dB SPL. So, using the impedance rating, one can calculate a corresponding RMS output voltage, then a corresponding output voltage level for the reference SPL of 86 dB. Then the headphone output gain is adjusted to produce the reference level when the reference tone is played back. This seems to work pretty well as the levels sound about right in comparison to speakers.

The difference in accuracy is presumably because the sensitivity rating is determined pursuant to the standard that uses a dummy head with microphones inside and is more nearly accurate to real HP use than my just sticking an SPL meter inside the phones.

Anyway, that's the plan. I'm curious if other folks use similar, calibrated monitoring gain systems with their HPs.

Cheers,

Otto
 
Jun 10, 2007 at 4:58 PM Post #2 of 4

ofajen

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Quote:

Originally Posted by ofajen /img/forum/go_quote.gif
The other needed step is to actually calibrate the HP levels to the same SPL reference level. I've tried an SPL meter inside the headphones to do the same sort of calibration, but I think I get more accurate results by simply using the sensitivity rating of the headphones to determine the appropriate output voltage level to produce the right signal level. Example: HD580 sensitivity is 1 mW produces 97 dB SPL. So, using the impedance rating, one can calculate a corresponding RMS output voltage, then a corresponding output voltage level for the reference SPL of 86 dB. Then the headphone output gain is adjusted to produce the reference level when the reference tone is played back. This seems to work pretty well as the levels sound about right in comparison to speakers.


Lest I cause confusion here, this latter type of calibration was done using 1 KHz reference sine tones, not a calibrated pink noise file, since the HD580's impedance varies significantly with frequency and this type of calibration requires knowing the exact value of the headphone's impedance.

Cheers,

Otto
 
Jun 10, 2007 at 5:17 PM Post #3 of 4

Skylab

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I guess I do. I use an SPL meter to keep my levels at 80db peak (A Weighted). But I use program material (stuff I know is "loud", i.e. recorded/mastered with very high levels), not sine waves or pink noise.
 
Jun 10, 2007 at 8:40 PM Post #4 of 4

ofajen

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Quote:

Originally Posted by Skylab /img/forum/go_quote.gif
I guess I do. I use an SPL meter to keep my levels at 80db peak (A Weighted). But I use program material (stuff I know is "loud", i.e. recorded/mastered with very high levels), not sine waves or pink noise.


That's enough to ensure you protect your ears and have roughly consistent levels. The extra level of precision I employ is mainly useful on the production side, since it gives mastery over the loudness of a mix and of the resulting master. And honestly, not all mastering engineers have adopted this practice, though I would hate to flounder around without it if that was how I made a living. Still, anyone who wants to listen critically to the difference of a small tweak or compare gear would do well to consider having this level of control over monitoring gain to ensure that volume differences are taken off the table.

Cheers,

Otto
 

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